The sperm whale has the largest brain on earth. The head, which also houses the spermaceti organ, occupies about one third of the sperm whale's body. The name sperm whale derives from the oil contained in the spermaceti organ, which early whalers thought looked like semen. In fact the spermaceti organ is used by whales to communicate, which is an important feature of this very sociable animal's life. Sperm whales are found across the globe, avoiding only ice packed oceans. They feed mainly on squid and fish. To catch this prey, sperm whales are able to dive up to 2km deep for 45 minutes at a time. Sperm whales were hunted between the early seventeenth and mid nineteenth century for their oil and this led to a massive decline in population numbers. Today, Japan is the only country which still continues to hunt this species.

Urgent Conservation Actions

Further research into the impact of human activities plus extending the network of marine protected areas to include more of the open water habitats used by sperm whales.

Early cetaceans are known from 50 million year old fossils found in India and Pakistan, along the ancient Tethys Sea which separated Africa from Asia and southern Europe. These early members of the cetacean clade (Ambulocetus, Indocetus, Pakicetus and Rodhocetus) were dolphin-sized amphibious mammals called archaeocetes, which vaguely resembled something between an otter and a crocodile. They had reduced hind limbs, but probably propelled themselves through the water using up-and-down movements of a strong tail, as do living cetaceans. It was long thought that these early whales were closely related to an extinct group of primitive carnivorous mammals called mesonychids, but molecular data now indicate that cetaceans are most closely related to hippos. Cetaceans are now grouped together with artiodactyls in a new clade, Cetartiodactyla. Around 50-35 million years ago the archaeocetes diversified and spread into deeper oceanic waters, with genera such as Basilosaurus and Dorudon well represented in the fossil record. By 30 million years ago, most of the archaeocetes were extinct, and two distinct new suborders had evolved, the mysticetes (baleen whales) and odontocetes (toothed whales).

There has been much debate as to whether the sperm whale belongs to the Mysticetes or Odontoceti whales. However, molecular studies place the sperm whale in the suborder Odontoceti along with the other toothed whales.

The Physeteridae family to which the sperm whale belongs to evolved about 25 million years ago before diversifying into several different species of sperm whale some 15 million years ago. Most of these species have since become extinct, leaving just three species of sperm whale surviving today. These are the sperm whale Physter macrocephalus, the pygmy sperm whale Kogia breviceps and the dwarf sperm whale Kogia simus. Since the kogiids, to which the pygmy and dwarf sperm whale belong, diverged from the Physeteroidea lineage 8 million years ago, the sperm whale Physeter macrocephalus is the most phylogenetically distinct of all species of living odontocetes.

Description

Size:

Adult Males: 15-18 m, Females:11 m

Weight: Males: 45 t, Females: 15 t

The sperm whale's large, box-shaped head makes up one third of its total body length, giving the animal an extremely distinctive appearance. This large head is home to the largest brain on earth and the massive spermaceti organ that gave the sperm whale its name. An S shaped blowhole is positioned at the top front of the nose above the spermaceti organ. Beneath the spermaceti organ is a powerful jaw that is outlined in white and contains two rows of large conical teeth. Behind the jaw are grooves that allow the throat to expand during feeding.

The dark grey or black skin that covers the head is relatively smooth while the rest of the body is covered in deep dimples. A small flipper is located on either side of the body which gradually narrows along its length to the tail flukes. Sperm whales have a low, rounded dorsal fin on their back. Mature females often have patches of white toughened skin, called calluses, on their dorsal fins, a character that enables them to be distinguished from other sperm whales.

Both sexes frequently have white marks and scars on their bodies which are the result of interactions with other sperm whales, predators such as killer whales or damage caused by ship collisions. The triangular tail fluke of the sperm whale is not particularly distinctive but along with the dorsal fin it is often the only part of the whale visible to observers above the surface of the water and is therefore used to identify this species. When observed from a boat the appearance of the sperm whale is often described as log like, which although somewhat crude and basic is a rather good description of a sperm whale swimming on the surface of the sea.

Ecology

The spermaceti organ occupies 25-33 per cent of the sperm whale’s head. This organ is full of spermaceti oil which people originally thought was semen, hence the name sperm whale. It is now thought that the spermaceti organ and its oil is used by whales for echolocation and communication. A sound, which is called a click, is produced by air being forced from the front of the spermaceti organ to the back where it is reflected off an air sac and directed into the water in front of the whale. Using clicks the sperm whale is able to communicate over tens of kilometers of water.

Sperm whales are extremely sociable mammals with females and juveniles travelling together in large groups of about twenty to thirty whales. Individuals are able to communicate vocally with one other and there is lots of physical contact. Living communally means that young are cared for by the entire group and provides protection from predators. For example, there have been accounts of sperm whales grouping together to deflect attacks from killer whales (Orcinus orca) and coming to the aid of individuals under attack.

The diet of the sperm whale is varied and a male can eat up to 1,000kg of medium sized fish and squid each day. They have also been known to eat crabs, jellyfish and sponges as well as rubbish they mistake for prey. The preferred food of sperm whale is squid and it is known to prey on giant squid, Architeuthis, which can be almost as large as the sperm whale.

To catch prey such as the giant squid the sperm whale has to dive deep into the ocean. Sperm whales generally dive to depths of 300 – 800m but have been known to dive between 1 and 2 km spending about 7 minutes at the surface between each dive which will last on average for 45 minutes.

The life of a whale begins in the womb where it grows for 15 months before being born. Calves are able to swim almost immediately and they will suckle milk from their mother for about two years. Young sperm whales remain with the social group to which their mother belongs. It is likely that females remain with this group throughout their lives but males gradually leave to pursue a solitary life, retuning to a female group only to mate. It is thought that the male prefers to be alone since a group of females will out-compete him in the search for food. Once a female reaches reproductive age, which can be as early as nine years old she will be able to produce a calf every 4-6 years until after 40 years of age when she will become pregnant less and less frequently. Males become sexually mature later than females once they are in their 20’s. Both sexes are able to live for more than 60 years with some females living until they are in their 80’s.

Habitat

Sperm whales are marine mammals and can be found in oceans across the globe between the latitudes of 400 in the south and 500 in the north. Females show a greater preference for warmer water than males and tend to stay within latitudes where the sea temperature is 150C or more. Males are often seen in much cooler regions, although they do avoid the iced packed areas such as at the poles. Rarely found in shallow water less than 1km deep, sperm whales can be found where there are deep sea canyons or steep drop offs near productive areas where there is plenty of food for them to eat.

Distribution

Found globally across all oceans between the latitudes of 40o in the south and 50o in the north.

It was estimated in 2003 that there were approximately 360,000 sperm whales. This is a 68% decrease in population size compared to the pre-hunting estimate of 1,110,000. Although this rapid decline ceased with the ban on commercial whaling, it is not yet known what long-term effect the disruption of social units has had on the sperm whale population.

Population Trend

Unknown.

Status

Classified as Vulnerable (VU A1d) on the 2010 IUCN Red List of Threatened Species

Threats

Historically, the primary threat to sperm whales was commercial hunting that occurred between the early 17th century and 1986 when the ban on commercial whaling began. The sperm whale was hunted for its spermaceti oil which was used to make candles and lubricate machinery. Early whalers hunted with basic equipment and travelled extensively to catch their prey. The intensity with which whales were hunted increased with the development of more sophisticated equipment that included specially designed ships that made it easier to haul whales onboard. Large males in particular were targeted and this naturally caused a decrease in the average size of males as well as a additional drop in pregnancy rate. In addition to the reduction in number of males, the loss of older females from the social group also meant the loss of knowledge and care for young from the group and the impacts of this loss on the group are yet to be understood.

Although commercial whaling was banned in 1986 by the International Whaling Commission (IWC), Japan resumed hunting of sperm whales in 2000 under the pretext of scientific research, which is permitted according to permits and quotas by the IWC. The whale carcasses caught are subject to scientific research before being sold for meat and other goods. The Japanese whaling industry continues to attract controversy but maintains its desire for commercial whaling to resume.

Humans and their use of the sea provide almost all the threats that face sperm whales in the modern age. Collisions with boats and entanglement in fishing equipment are both causes of mortality, with fishermen beginning to show hostility towards sperm whales that eat their catch and damage their equipment.

There is conflicting evidence on the effect of sonar signals and seismic pulses used by the military and companies searching for oil. Some studies have found that sperm whales leave areas or change their behaviour when confronted with the noise produced by sonar and seismic surveys. However it is not yet known what effect noise pollution has on the communication abilities of sperm whales and noise may also be having negative impacts on sperm whale feeding and mating opportunities.

The accumulation of toxic metals in sperm whales is also a concern. As predators at the top of a food chain the potential for accumulation of toxins through the food chain is high. Sperm whales have been found with concentrations of mercury and cadmium that would prove toxic to smaller mammal species, and while this so far has been a concern of humans who eat whale meat it is not yet understood what effect a build up of such metals has on the sperm whales themselves.

Like all species, sperm whales are threatened by the changing climate that is being accelerated by human activities. As climates change the ocean will become warmer and weather patterns will alter, potentially affecting the areas in which sperm whales are able to find their resources. Although sperm whales make use of an extremely wide geographic range and should be able to adapt to changes there is concern that they will not be able to keep up if conditions change too rapidly.

Conservation Underway

The sperm whale is listed on CITES Appendix I which prohibits the trade of threatened species, and on Appendix I of the Convention on Migratory Species.

The International Whaling Commission, consisting of 88 member countries from across the world, was set up in 1946 to regulate the whaling industry. In 1986 a decision was made to ban commercial whaling in response to declining whale population numbers. Whale hunting is now only permitted for aboriginal subsistence and scientific research. The IWC sets quotas for the number of sperm whales a nation is permitted to catch. Currently Japan is the only nation still hunting sperm whales for scientific research. This must be carried out according to regulations.

The IWC has also set up two whale sanctuaries, the Indian Ocean Sanctuary and Southern Ocean Sanctuary where, despite sanctuary status, Japan continue to catch other species of whales.

In order to minimize the disruption of seismic surveys to all cetaceans, survey ships are required to carry onboard Marine Mammal Observers who will observe and listen for marine mammals such as sperm whales in areas in which seismic surveys are being conducted. If a sperm whale is observed within 500 m of a survey vessel, seismic activity cannot begin until the animal has moved away.

Conservation Proposed

Considering the massive decline in population size as a result of commercial hunting it is essential that the ban set by IWC remains in place as any resuming of hunting activity will be hard to monitor and regulate, and would inevitably lead to another drastic decline in sperm whale numbers.

Currently just 1.17% of marine habitats are protected and of these, only a small proportion is open water. Although it is difficult to contain sperm whales within a certain area, networks of protected areas would allow the safe migration of these mammals and protect the principle places in which they are found, or the habitats which have high productivity of the food resources they require. To improve the effectiveness of the existing Southern Ocean Sanctuary as a marine protected area it has been proposed that formal goals and a management plan be developed and put into place.